We have developed a set of tools for rapidly mapping disufide bonds in proteins. The strategy involves extensive cleavage of the protein of interest with enzymes under conditions that prevent breakage or interchange of disulfide linkages; followed by analysis of the resulting fragments by MALDI-ion trap mass spectrometry. We have used the technique to successfully map growth factors, proteinaceous toxins, and an analogue of the human LDL receptor. A paper describing this work has been published Qin and Chait, Anal. Chem. 69, 4002-4009, 1997.